The overall objective is to establish an in vitro system to permit detailed study of fluoride, particularly at low levels, on developing mammalian tooth germs. Information will be sought at the light microscope and ultrastructural levels of effects of fluoride on ameloblasts, odontoblasts including developing stages. Cellular effects will be investigated in relation to effects on early dentinal and enamel matrix secretion as a response to fluoride. A primary aim is to investigate why ameloblasts are exquisitely sensitive to fluoride at doses as low as 1 ppm when considerably higher doses are required for observable effects in bone or other tissues. The advantage of this system is that it will permit study of fluoride at very low known doses in stages before mineralization, heretofore impossible in animals. Principle objectives are to determine: (1) Observable effects at fluoride levels ranging downwards from 100 ppm. (2) The minimal duration required for fluoride activity at a range of fluoride levels.